Metal Oxide Composites Research Articles

Controllable synthesis of Bi2O3-MoO3 binary system metal composite oxides and structure–activity relationships for aerobic oxidative desulfurization

Controllable synthesis of Bi2O3-MoO3 binary system metal composite oxides and structure–activity relationships for aerobic oxidative desulfurization

Sulfite activation by Jahn-Teller-driven oxygen vacancies Cu-Mn composite oxide for chlortetracycline degradation

Copper-manganese composite metal oxides (CuMnOy) were prepared by hydrolysis-driven oxidation-reduction method and used to activate sulfite to degrade chlortetracycline hydrochloride (CTC) for the first time. The Jahn-Teller ions Mn3+ and Cu2+ exist in CuMnOy, which form a solid electric charge transport redox system and ensure the continuous generation of reactive oxygen species (ROS). Through the systematic study of the experimental parameters such as sulfite concentration, catalyst metal molar ratio, catalyst amounts and initial pH, the optimal degradation rate of CTC could reach 91.74% within 10 min and 94.46% after 30 min. The major reactive radicals were determined by radical quenching experiments and electron paramagnetic resonance (EPR) trapping techniques, and it was confirmed that SO4•- and •O2- played a nonnegligible role in the process of degrading CTC. Density functional theory (DFT) calculations show that higher Fukui indices (f- and f0) of CTC sites are more vulnerable to free radical attack. CuMnOy has low CTC degradation intermediate toxicity, high catalytic performance, good anti-interference ability, reusability and stability, and possesses decent application potential in the actual water treatment field.

Tuning the phase structure and surface morphology of Cr2O3:CuO thin film by annealing for enhanced ammonia sensing performance at room temperature

Driven by global environmental concerns, there is currently a strong need to identify real-time sensing materials for sensor devices. In this work, we mainly report the observation of an annealing-induced enhancement in room temperature ammonia sensing performance of binary composite metal oxide thin films of Cr2O3:CuO by tuning the phase structure and surface morphology. The activation energy of Cr2O3:CuO film was estimated from the Arrhenius plot and its magnitudes varied between 0.182 eV and 0.186 eV upon the variation of annealing temperature from 300 to 1000 °C. X-ray diffraction patterns of annealed Cr2O3:CuO film showed the existence of two different phases such as tetragonal CuCr2O4 and orthogonal CuCrO4. Fascinatingly, the CuCr2O4/CuCrO4 thin film prepared on quartz substrate exhibits a clearly visible cumin seed-like morphology with clear boundaries, which support the observed improvement in gas sensing performance. The sensitivity and detection limit (DL) of CuCr2O4/CuCrO4 thin film for ammonia gas were measured to be 5.77 and 1.9 ppm, respectively. The CuCr2O4/CuCrO4 film shows good response to different concentrations of NH3 and the film has a competence to retort for very low NH3 level (1 ppm). In addition, the prepared film retains 95 % of its initial response to ammonia even after 1-year duration. The observed results provide a probe for designing good and reliable room temperature sensor for ammonia gas at room temperature.

Insights into effects of grain boundary engineering in composite metal oxide catalysts for improving catalytic performance

Volatile Organic Compounds (VOCs) have long been a threat to human health. However, designing economical and efficient transition metal composite oxide catalysts for VOCs purification remains a challenge. Herein, this study demonstrates the enormous potential of grain boundary engineering in facilitating VOCs decomposition over ordered mesoporous composite oxide denoted as 3D-MnxCoy (x, y = 1, 3, 5, 7, 9). Specifically, the three-dimensional (3D) Mn7Co1 catalyst shows 100% ethyl acetate removal efficiency for a continuous airflow containing 1000 ppm ethyl acetate over 60000 h−1 space velocity at 160 °C. Mechanism study suggests that the high catalytic performance originates from the lattice distortion caused by the introduction of heteroatoms, along with the size effect of nanopore walls, which leads to the formation of various grain boundaries on the catalyst surface. The presence of grain boundaries facilitates the generation of oxygen vacancies, thus promoting the migration and activation of oxygen species. Furthermore, the near-atmospheric pressure X-ray photoelectron spectroscopy (NAP- XPS) monitoring results reveal that the bimetallic synergy enhanced by grain boundary accelerates the catalytic reaction rate of VOCs through Mn3++Co3+↔Mn4++Co2+ redox cycle. This study may shed light on the great potential of ordered mesoporous bimetallic oxide catalysts in VOCs pollution control.

Highly efficient Cd(II) removal from groundwater utilizing layered mixed metal oxides-graphitic carbon nitride composite with improved cycling stability

Graphitic carbon nitride (GCN) and its mixed metal oxide (MMO) composites are synthesized via co-precipitation followed by the pyrolysis method using various ratios of calcium aluminium (Ca:Al) with GCN, to enhance the adsorption ability towards Cd(ii) present in wastewater. Synthesized composite materials were characterized using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) surface analysis, Fourier transforms infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) analyses. Due to its higher specific surface area (218.65 m2/g), the produced GCN and CaAl mixed metal oxide composite (GCN-MMO) exhibits improved adsorption ability towards Cd(II) ions. Approximately >99 % were adsorbed with Langmuir qmax of 131.57 mg/g. An overall pseudo-second-order (PSO) model fitted the kinetics data well. The possible mechanisms were surface complexation and precipitation, outer-sphere complexation, and acid-base mechanism. Further, the groundwater application was studied, and it achieved adsorption below the maximum permissible limit of USEPA with excellent cycling stability. The findings of this study showed that GCN-MMO composite material may be useful for the adsorption of Cd(II) heavy metal from an aqueous solution.

Synthesis of NiO/TiO₂ Binary Nano Composite for the Enhancement of Gas Sensing Properties

The rapid development of electronic devices used in detecting noxious gases has made gas sensors more and more important. The semiconducting metal oxides’ ability to detect gases is a result of their reactions with the gases in the environment, which change the semiconductor’s resistance. In this study, a composite metal oxide material made of NiO and TiO2 with different doping concentrations of (1, 3, 5, 7) is synthesized using the sol-gel process. A binary compound with excellent crystallization is obtained post 500° calcination. SEM, XRD and FTIR were used to evaluate the morphological fluctuations and the phase identification of NiO/TiO2 nano composite. The butane gas is found to respond well in the concentration ranges of 500 to 3000 ppm, respectively, at temperatures 373 to 573 K as well as at ambient temperature.

Investigations on substituted Si-doped Mn2O3/Mn3O4 redox pair for thermochemical energy storage

Next-generation concentrated solar power plants with thermochemical energy storage can meet the demand for peak regulation and power supply, which stimulates the development and application of low-priced metal oxide thermochemical thermal storage materials. Mn-based composite metal oxide is a competitive candidate for large-scale applications given its character of being non-toxic, cheap, and highly efficient. However, the utilization of pure Mn2O3 suffers from sintering, which limits its re-oxidation and hence affects the applicability. In this study, Si is introduced to solve the above problems and improve the reaction characteristics of pure Mn2O3. (Mn1−xSix)2O3 is synthesized by substituent doping, with the best performance at x = 3 % and 5 %, reaching 96.18 % and 94.71 % of reduction conversion rate, respectively. The performance decay of the (Mn0.95Si0.05)2O3 sample was tested and evaluated, with reduction conversions of 90.92 % and 63.64 % after 50 and 300 cycles, respectively. A series of characterization results confirm that Si4+ is successfully doped into the Mn2O3 lattice, introducing defects into the crystal structure, which is favorable for the oxidation reaction. Density functional theory calculations of oxygen adsorption/dissociation and oxygen diffusion indicate that the doped Mn-Si oxides have lower reaction potentials and energies, which explains the promotion of the re-oxidation reaction by Si. By investigating the thermochemical energy storage properties and mechanism of Mn-Si composite metal oxides, we provide guidance for large-scale, cheap, and eco-friendly energy storage applications.

Synthesis, characterization, and enhanced sunlight-active photocatalytic property of single-site octahedral iron(III) oxide complex – Grafted graphene oxide

The reported study delves into the synthesis and analysis of an innovative composite material formed by grafting single-site octahedral iron(III) oxide complex onto graphene oxide (GO). The formation of the composite employs an innovative approach, utilizing a one-pot adsorption procedure to synthesize iron(III) oxide complex-modified graphene oxide (Fe-GO), with [Fe(bipy)Cl4][bipyH] serving as the precursor complex. Employing an array of analytical techniques including XRD, FTIR, DRS, PL, SEM, EDAX, XPS, and MB analyses, we meticulously uncover the intricate structural attributes of the resulting Fe-GO composite. Mössbauer spectroscopy confirms the presence of distorted octahedral Fe3+ single-sites grafted onto the GO surface, a crucial aspect firmly established in our synthesized specimen. This innovative approach not only enhances the photoactive properties of GO but also offers a resource-efficient avenue for such improvements. The photochemical efficacy of the synthesized samples is rigorously assessed by Rhodamine B degradation in water under authentic sunlight exposure. Remarkably, the Fe-GO composite outperforms pristine graphite, GO, and metal oxide photocatalysts (TiO2 and SnO2 based materials), underscoring its exceptional photocatalytic performance. The catalyst's durability and recyclability are thoroughly examined over five cycles, affirming its lasting effectiveness. Collectively, our findings highlight the substantial promise of iron-complex-decorated GO as an efficient solar-responsive photocatalyst, surpassing existing commercially available counterparts. This investigation opens a viable path towards the development of economically sustainable photocatalysts, tailored to meet the demands of various environmental applications reliant on solar-driven reactions.

Preparation and application of Ag–Ce–O composite metal oxide catalyst in catalytic ozonation for elimination of Reactive Black 5 dye from aqueous media

It is necessary to treat textile effluents before discharging them into natural water bodies as they harm the environment. Compared to conventional treatment methods, catalytic ozonation has gained attention due to its effectiveness in removing refractory organic pollutants. In this study, the coprecipitation method was used to synthesize a composite metal oxide of silver and cerium oxide, and the synthesized catalyst was used to eliminate the Reactive Black 5 (RB5) dye. X-ray diffraction, scanning electron microscopic, and Brunauer–Emmett–Teller surface area analyses were performed to characterize the synthesized catalyst. Afterwards, relevant experimental parameters, such as pH, ozone and catalyst dosages, and initial dye concentration, were investigated. The experiments revealed that the optimal experimental conditions were a pH value of 10, a catalyst dosage of 0.7 g/L, and an ozone dosage of 60 L/h. In these optimized conditions, the RB5 dye was entirely removed, and a chemical oxygen demand removal efficiency of 88% was achieved within a reaction time of 80 min. Furthermore, the recycling potential of the catalyst was tested for three cycles, and no deterioration in its activity was observed. Additionally, studies were conducted using a hydroxyl radical scavenger in order to understand the reaction pathway of the system. As a result, the indirect pathway was more dominant than the direct pathway in the system.

Fabrication of cobalt-zinc bimetallic oxides@polypyrrole composites for high-performance electromagnetic wave absorption

Composite materials that combine magnetic and dielectric losses offer a potential solution to enhance impedance match and significantly improve microwave absorption. In this study, Co3O4/ZnCo2O4 and ZnCo2O4/ZnO with varying metal oxide compositions are successfully synthesized, which are achieved by modifying the ratios of Co2+ and Zn2+ ions in the CoZn bimetallic metal–organic framework (MOF) precursor, followed by a high-temperature oxidative calcination process. Subsequently, a layer of polypyrrole (PPy) is coated onto the composite surfaces, resulting in the formation of core–shell structures known as Co3O4/ZnCo2O4@PPy (CZCP) and ZnCo2O4/ZnO@PPy (ZCZP) composites. The proposed method allows for rapid adjustments to the metal oxide composition within the inner shell, enabling the creation of composites with varying degrees of magnetic losses. The inclusion of PPy in the outer shell serves to enhance the bonding strength of the entire composite structure while contributing to conductive and dielectric losses. In specific experimental conditions, when the loading is set at 50 wt%, the CZCP composite exhibits an effective absorption bandwidth (EAB) of 5.58 GHz (12.42 GHz-18 GHz) at a thickness of 1.53 mm. Meanwhile, the ZCZP composite demonstrates an impressive minimum reflection loss (RLmin) of −71.2 dB at 13.04 GHz, with a thickness of 1.84 mm. This study offers a synthesis strategy for designing absorbent composites that possess light weight and excellent absorptive properties, thereby contributing to the advancement of electromagnetic wave absorbing materials.

Galvanic Replacement Reaction: Enabling the Creation of Active Catalytic Structures.

The galvanic replacement reaction (GRR) is recognized as a redox process where one metal undergoes oxidation by the ions of another metal possessing a higher reduction potential. This reaction takes place at the interface between a substrate and a solution containing metal ions. Utilizing metal or metal oxide as sacrificial templates enables the synthesis of metallic nanoparticles, oxide-metal composites, and mixed oxides through GRR. Growing evidence showed that GRR has a direct impact on surface structures and properties. This has generated significant interest in catalysis and opened up new horizons for the application of GRR in energy and chemical transformations. This review provides a comprehensive overview of the synthetic strategies utilizing GRR for the creation of catalytically active structures. It discusses the formation of alloys, intermetallic compounds, single atom alloys, metal-oxide composites, and mixed metal oxides with diverse nanostructures. Additionally, GRR serves as a postsynthesis method to modulate metal-oxide interfaces through the replacement of oxide domains. The review also outlines potential future directions in this field.

Catalytic regeneration of amine-based absorbents for CO2 capture: The effect of acidic sites and accessibility

The high regeneration energy consumption is the bottleneck problem for the large-scale application of organic amine absorption method. Catalytic regeneration has received a lot of attention because it can be done at low temperatures using solid acid catalysts. Although the catalytic activity of the catalysts presently reported is exceptional, the exorbitant cost renders this technology unsuitable for industrial implementation.The present work uses a composite metal oxide solid acid catalysts for the catalytic regeneration of a CO2-rich 5 M MEA solution at 90 °C. The findings indicate that the inclusion of SO42-/ZrTiOx catalyst resulted in a 99% increase in CO2 desorption rate, a 43% improvement in cyclic capacity, and a 29.09% reduction in relative heat duty when compared to the blank experiment. The catalyst underwent characterization through BET, NH3-TPD, and Py-IR techniques, revealing that its superior catalytic performance can be attributed to its substantial mesoporous specific surface area and significant concentration of acid sites. The catalytic effect and catalytic mechanism of SO42-/ZrTiOx were confirmed using 13C NMR spectroscopy. The stability of the SO42-/ZrTiOx catalyst during regeneration was investigated in five cycles and the cause of catalyst deactivation was investigated by FT-IR. The results show that the SO42-/ZrTiOx catalyst has high catalytic activity and low cost, and has potential for large-scale industrial applications.

One-pot synthesis of NH2-MIL-101(Fe) and α – Fe2O3 composite as efficient heterojunction for multifunctional photocatalytic membranes: Towards zero waste generation

Here in, one-pot synthesis of amine functionalized iron-based Metal-Organic Framework (MOF) namely NH2-MIL-101(Fe) is systematically tuned such that it also results in formation of morphology-oriented iron-oxide (α-Fe2O3) along with MOF, without adding any additional precursor. Ligand deficiency facilitates the free amine group of ligands to drive the formation of metal oxide (MO). This composite of MO and MOF behaves as a heterojunction that efficiently separates charge carriers and allows good photocatalytic activity, with more than 95 % degradation of methylene blue (MB) dye. The composite was then integrated into nanofiber membranes for water treatment, it resulted in overall 94 % rejection, with 20 % of MB being degraded simultaneously during this rejection and, this can be considered as fairly good for an emerging process that comprises of simultaneous degradation and separation. The new thermally stable and self-cleaning heterojunction MOF membranes developed in this study have sparked hopes as promising materials for near to zero waste generation in water treatment.

Exceptional arsenic removal using novel mesoporous Mg-Al-Ti ternary composite oxide nanoparticles prepared via self-assembly templating method

Arsenic contamination of water through natural and anthropogenic activities is a grave problem today. One of the most efficient ways to remove arsenic from water is through adsorption. Porous nanomaterials show high adsorption capacities due to high surface area, and efficient mass transfer with plenty of active adsorption sites. Porous metal oxides have been successfully employed to remove arsenic from water previously. However, ternary metal oxide composites hold potential for novel adsorbent materials but have yet to be explored in depth. Mesoporous Mg-Al-Ti oxide composite oxide nanoparticles with varying compositions were synthesized via a low-cost, scalable, evaporation-induced self-assembly technique using P123 block copolymer as a soft template. All the compositions of synthesized ternary oxide nanoparticles exhibited exceptionally high arsenic adsorption capacities ranging from 543 to 1215 mg/g for As(V) and 359.6–919.4 mg/g for As(III) along with 96–98% removal of arsenic from real groundwater samples of up to 489.3 ppb. The composites show mesopores and high surface area ranging from 93-393.6 m2/g with very small particle size ranging from 8 to 12 nm. The nanoparticles have shown great selectivity towards arsenic and exceptional adsorption performance in a wide pH range. High volume-to-surface area ratio, an abundance of hydroxyl groups, interconnected mesoporous morphology, and high point of zero charge pH contribute to the high adsorption capacity of the composite oxides. Mesoporous Mg-Al-Ti ternary oxide composite nanoparticles have shown higher adsorption capacity towards arsenic than many existing adsorbent material materials and can be a very promising candidate for arsenic remediation from water.

The Old Polyoxometalates in New Application as Molecular Resistive Switching Memristors

AbstractThe coming big‐data era has created a huge demand for next‐generation memory technologies with characters of higher data‐storage densities, faster access speeds, lower power consumption and better environmental compatibility. In this field, the design of resistive switching active materials is pivotal but challengeable. Polyoxometalates (POMs) are promising candidates for next‐generation molecular memristors due to their versatile redox characters, excellent electron reservoirs and good compatibility/convenience in microelectronics processing. In this review, five kinds of POM‐based active materials in nonvolatile memories (inorganic POMs, crystalline organic‐inorganic hybrid POMOFs, polymer modified POMs, POM/transition metal oxides composites and the deposition of POM on metal surfaces) were described. The components of POMs active materials, device fabrications, device parameters, and resistive switching mechanisms relative to their structures were summarized. Finally, challenges and future perspectives of POMs‐based memristors were also presented.

Preparation of rGO/NiO nanocomposites by AC and nanosecond pulsed DBD

Graphene/transition metal oxide composites combine the energy-storing mechanisms of pseudo-capacitance and double layer capacitance, and are considered as preferred electrode materials for supercapacitors. For the composites' complex structure and components, it is important to develop a method with good controllability to monitor the structure and component of the nanocomposites, which is critical for the electrochemical performance optimization and the further industrial application. In this paper, graphene oxide (GO) and nickel acetate tetrahydrate (Ni(CH3COO)2·4H2O) were used to prepare reduced graphene oxide/nickel oxide (rGO/NiO) nanocomposites utilizing dielectric barrier discharge (DBD) plasmas with AC and nanosecond (ns) pulse power supplies. The scanning electron microscope (SEM), Raman spectra, X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) are used to study the nanocomposites created under various discharge conditions. It shows the splitting and delamination of the prepared composites surface, a rise in ID/IG, and the reduction of GO after plasma treatment result in an excellent connection with the electrode material surface and electrolytic solution, and good capacitor performance. The rGO/NiO nanocomposites prepared by AC DBD have better charge transfer resistance, conductivity, and electrochemical capacitance retention rate than the materials prepared by ns pulsed DBD, which is analysed by power deposition and thermodynamics. The work contributes to reveal the mechanism of plasma material preparation, which will give new impetus to the development of environmental-friendly method for electrode materials preparation.

Magnetic and ultrasonic integrated photocatalytic hydrogen evolution effects with Nanosize CoOCu2OZnO and TiO2 decorated on reduced graphene oxide

In this study, metal oxide composite (CoOCu2OZnO) and TiO2 on graphene oxide composite (CCZ−G−T) were synthesized to improve visible light-driven H2 evolution through the addition of a cation scavenger, ultrasonic effect, and magnetic field effect. The synthesized nanocomposites were characterized through structural, surface, and electrochemical analyses with band structure. The photocatalyst showed hydrogen production of 792 μmol·g−1 for 4 hours. Moreover, this CCZ−G−T photocatalyst exhibits relatively high photocatalytic activity at (530−810) μmol·g−1 when using a scavenger, 1,190 μmol·g−1 when using a magnetic field of 0.14 T, and 1,230 μmol·g−1 when using ultrasonic waves. The CCZ−G−T composite exhibited 630 μmol·g−1 under a magnetic field condition of 0.14 T for 1 hour, which was significantly higher than the hydrogen production rate of 510 μmol·g−1 under ultrasonic conditions. The current study provides new insights into the magnetic field effect on the hydrogen evolution reaction (HER) of graphene-based photocatalysts.

Pt-Loaded Nb─W Metal Composite Oxide for Selective Cleavage of Secondary C─O Bonds.

Selective hydrogenolysis of glycerol to 1,3-propanediol (1,3-PDO) is recognized as one of the most promising reactions for the valorization of biomass. Precise activation of C─O bonds of glycerol molecule is the key step to realize the high yield of catalytic conversion. Here, a Pt-loaded Nb-W composite oxides with crystallographic shear phase for the precise activation and cleavage of secondary C─O (C(2)─O) bonds are first reported. The developed Nb14 W3 O44 with uniform structure possesses arrays of W-O-Nb active sites that totally distinct from individual WOx or NbOx species, which is superior to the adsorption and activation of C(2)─O bonds. The Nb14 W3 O44 support with rich reversible redox couples also promotes the electron feedback ability of Pt and enhances its interaction with Pt nanoparticles, resulting in high activity for H2 dissociation and hydrogenation. All these favorable factors confer the Pt/Nb14 W3 O44 excellent performance for selective hydrogenolysis of glycerol to 1,3-PDO with the yield of 75.2% exceeding the record of 66%, paying the way for the commercial development of biomass conversion. The reported catalysts or approach can also be adopted to create a family of Nb-W metal composite oxides for other catalytic reactions requiring selective C─O bond activation and cleavage.

Crystallography of a new Mn(V,Ti,Al)2O4 compositionally complex spinel oxide in a BCC compositionally complex alloy

The concept of compositionally complex alloy (CCA) has recently been applied in developing compositionally complex oxide (CCO). In this contribution, we discovered a new CCO with a spinel structure that is embedded in a new body-centered cubic CCA matrix. The crystal structure of the newly found CCO is characterized by neutron diffraction and high-resolution transmission electron microscopy. It is found that the chemical formula of the new CCO is Mn(V,Ti,Al)2O4, where the Mn atoms occupy the tetrahedral position while the V, Ti and Al atoms share the octahedral sites. The elements that take the octahedral sites are interchangeable. The mechanical behavior was characterized by nano-indentation experiments and the localized strength of CCA is effectively promoted with the existence of CCO. The present work illustrates that the combination of new CCO with new CCA matrix could be a new strategy to develop new oxide-metal composites.

Preparation of metal oxide-loaded nickel foam adsorbents modified by biochar for the removal of cationic dyes from wastewater

In this study, metal composite oxides grown on nickel foam were prepared, which were modified by dopamine and biochar to obtain cauliflower-shaped Co2MnO4/[email protected]/BC adsorption material to adsorb cationic dyes from aqueous solutions. The maximum adsorption amounts qmax for methylene blue (MB), malachite green (MG), and crystal violet (CV) were 8.44, 41.03 and 3.39 mg g−1, and the adsorption aligned with the Langmuir isothermal model as single molecular layer adsorption on a homogeneous surface. The adsorption experiments of dyes were conducted using lake water in the environment, and the adsorption rates of MB, MG, and CV were 91.4%, 94.8% and 85.1%, respectively. Meanwhile, the material has wide pH applicability (3–9), and good adsorption-desorption cycle performance. In addition, the synthesized adsorbent Co2MnO4/[email protected]/BC and the control adsorbent were investigated and shown to have good adsorption capacity. In conclusion, the adsorbent materials synthesized in this work have some application prospects in dye wastewater adsorption.